Harmonic analyzer



Ase

amaai Mu. 14, 1933 UNITED STATES PATENT. OIF'FICE WARREN A. HARRISON, 0F HAPLEWOOD, NEW JERSEY, ASSGNOB T0 BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK EABIONIC AN ALYZEB,

Application led August 27, 1931. Serial No. 559,805.

It is useful for many purposes to know what components of harmonic frequencies are present in a wave, for instance an electric wave, and to know the amplitudes and phase relationships of these components. The ob'ect of this invention is to provide means or, and a method of, obtaining this information.

A feature of one species of this invention is the use of a disc whose periphery has been out to represent, in polar coordinates, the wave to be analyzed.

A feature of another species of this invention is the use of a cylinder whose vrim has been cut to represent the Wave to be analyzed.

In the system described herein the periphery of a disc is cut to represent the wave in polar coordinates so that one complete c cle of the wave to be analyzed is represente by the entire periphery of the disc. This disc is mounted on a shaft vand -rotated between a source of light and a'photoelectric cell, so that the light falling on the cell corres onds exactly to the wave? form to be'ana Ized. The output from the photoelectric cell t erefore is an electric" wave having Va. fundadise in revolutionsv per second and the same-harmonicv content as the original wave.

If the output from the photoelectric cell passes into a detector tuned for, say, 10() cycles, and if the disc is rotated at 100 revo-1 lutions er second the out ut from the detector willl bel a measureo the amplitude of fundamental in the original wave. If the disc is rotated at 50 revolutions per second, the 100 cycle componentimeasured will be the second harmonic of the original wave. If the disc is rotated at a revolutions per second, the 100 cycle component measured will be the nth harmonic of the original wave.

In an alternative arrangement the rim of a cylinder is cut to represent the wave in rectan lar coordinates, and the photoelectric ce may be placed inside the cylinder while the source of light is outside the cylinder, so that the rim of the cylinder varies the light beam in accordance with the wave to be measured.

In order to determine the phase and am- Fig. 2 is a graphical representation of one "55 cycle of the wave to be analyzed;

.Fig 3l isa front elevation of the disc, showlng its periphery cut in accordance with the wave of Fig. 2;

Fig. 4 is a schematic diagram of that 70 part of Fig. A1 including the circuit of the photoelectric cell land the circuits following, withy a tuned oscillograph substituted for the meter;

' Fig. 5 is a graphical representation of the 75 fundamental (or first armonic) of the vvf wave as. it would be recorded on the oscilloment'al frequency equal to the speed of the having f graph;

Fig.; 6 is a graphical representation of the second harmonic component;

l ."Fig.v 7 "is a graphical representation of the third harmonic component; and

.[Fig.`8 is a diagram, artly in section, of a cylinder of the invention showing the photoelectric cell and circuits following.

Inthe system of Fig. 1 a strip source of light l is focused by a lens 2 on a disc 3, forming a narrow strip image thereon. The disc, which is driven by a motor M has its periphery cut in accordance with Fig. 3 to represent the wave to be analyzed, in polar coordinates.

If only a single period of the wave to be analyzed -is represented on the disc it is driven at such a speed that the harmonic 9 under consideration has the frequenc for which the filter is selective. That is, 1f the iilter is selective at cycles per second and it is desired to measure the fundamental ofthe wave, the disc is driven at 100 revolus 'per second. lf it is desired to measure the second harmonic the disc is driven at 50 cycles per second and this harmonic will u have a frequency of 100 cycles per sec- .d and may be measured, etc. if more than a single period is represend the disc is driven correspondingly cr. That is, if two eriods are represented it is driven one ha f as fast, if three periods are represented one third as fast, etc. A photoelectric cell 4; is mounted behind the disc :trom the light source, so that it receives a varying amount of light depending on the amount of the disc which is cut away. A fluctuating current is thus produced in the cell. This current is amplied in the amplilier A and passed through a filter selective at a fixed frequency, say, 100 cycles. The ilter may be a mechanical f iilter such as that disclosed in United States Patent 1,708,945 issued April 16, 1929 to di. W. Horton, for example. A meter 5 is connected in the output circuit of the filter for indicating the value of the current in this circuit. When the speed of the disc is 100 revolutions per second, the meter reading proportional to the content of fundamental in the original Wave. The disc is then rotated at one half this speed and the meter reading indicates the amount of current of the second harmonic present in the wave. The disc is then rotated at one third this speed and the meter indicates the amount of current of the third harmonic present. The process may be continued until the Wave has been analyzed suiiciently for the purposes of study.

it it desired to make a graphical representation of the phase and amplitude of each component present in the Wave under investigation, the lilter F and meter 5 may be replaced by a tuned oscillograph, as shown in Fig. 4.

in the operation of the system of Fig. 4 all the elements of the system of Fig. 1 are used in the manner described in connection with that figure up to and including the amplifier A. Following the amplifier is a tuned oscillograph comprising a coil 6 and ay mechanical vibrating element 7 having attached thereto a mirror 8. A beam of light from a light source 9 is ldirected toward the mirror through a. lens 15 and reflected through a slit 10 onto a roll of film in a ilm boi: 11. When the disc is rotating at full speed it- Will then make an oscillograph record of the fundamental component such as that shown in Fig. 5, at one half speed it will make a record of the second harmonic component such as that shown in Fig. 6, and at one third speed it Will make a record of the third harmonic component such as shown in Fig. 7, etc. Suitable contact mechanism may be provided on the motor for making a mark on the record for each revolution of the dise, such as mark 16 (Figs. 5, 6 and 7). The record will then indicate the amplitude and phase of each component.

Fig. 8 shows an alternative arrangement in which a cylinder 12 has its rim lcut to represent the Wave to be analyzed. The cylinder is rotated by motor M through gear 13. The photoelectric cell i may be placed inside the cylinder, so that only one edge of the cylinder is between it and the light source. The impulses in the cell are amplified in the amplifier A, filtered in the filter F and measured in the meter 14 as in Fig. 1. The cylinder may be made by lirst making an ordinary oscillogram of the Wave to be analyzed, Wrapping it around the cylinder, and cutting the rim of the cylinder down to the Wave.

The oscillograph shown in Fig. 4 may of course be substituted for the meter 14 in this alternative arrangement.

impulses to mark each cycle of the Wave on the film, when the oscillograph is used may be obtained by suitable Contact mechanism on the motor, or in any other manner desired.

It is to be understood of course that many alternatives are available for the auxiliary apparatus described herein and that many changes may be made in the design of apparatus to perform the function described Without departing from the scope of my invention.

What is claimed is:

1. A Wave analyzer comprising in combination a source of light, a light responsive device, a disc between said source and said device Whose periphery has been cut to represent a Wave to be analyzed in polar coordinates, means for rotating said disc sequentially at speeds proportional to the frequencies of the wave component in the Wave to be analyzed, and means for obtaining an indication of the current in said light responsive device.

2. A Wave analyzer comprising an element Whose periphery has been cut to correspond with a Wave to be analyzed, means for turning said element, and means for obtaining an indication of the relative value of the fundamental and harmonic components present in said Wave.

3. A wave analyzer comprising an eleelement Whose periphery has been cut to correspond with a wave to be analyzed, said element being of disc shape, means for turning said element, and means for obtaining an indication of the contour of its periphery.

4. A Wave analyzer comprising an element Whose periphery has been cut to correspond With a Wave to be analyzed, said element being of cylindrical shape, means for turning said element, and means for obtaining an indication of the contour of its periphery.

5. A wave analyzer com rising in combination a light source, a ight responsive device, a cylindrical member whose rim has been cut to represent a Wave to bev anal zed interposed between said source and sai def vice, means for rotating said member at a. speed proportional to a component frequency of the wave to be analyzed, and means for obtaining an indication of the current in said light responsive device.

6. A wave analyzer comprising a rotatable element Whose boundary in a plane normal to the axis of rotation has been made to conform in shape with a Wave to be analyzed, means for rotating said element, and means for obtaining an oscillogra h record of each component of the wave un er analysis.

7. A Wave analyzer comprising a disc shaped element Whose perip ery has been out to correspond with a wave to be analyzed, means for turning said element, and means for obtaining an oscillograph record of each component of the Wave under analysis.

8. A Wave analyzer comprising a cylindrical element Whose rim has been cut to correspond with a wave to be analyzed, means for turning said element, and means for obtaining an oscillograph record of each component of the wave under analysis.

lili

9. The method of analyzing a wave whose form is known which consists in making av cast having undulations corresponding to said wave form, rotatin said cast at a speed proportional to a given armonie component of the Wave to be analyzed, projecting light through said undulations, and translatlng the light projectin through said undulation into correspon ing electrical variations.

10. A Wave analyzer comprising in combination a source of light, a light responsive device, an element whose rim has been cut to re resent a Wave to be anal zed interpose between said source of li t and said light responsive device, means or focusing light from said source on said element means for turnin said element at a, speed proportional to te frequency of the component to be analyzed, means for amplifying the impulses in said light responsive device, a filter connected to said amplifying means, and means for recording the Wave passing through said filter.

ln Witness whereof, I hereunto subscribe my name this 26 day of August 1931.

WARREN A.. MARRISN. 

